This application is for support of collaborative research conducted by a U.S. Principal Investigator (Angeles B. Ribera) and a Foreign Scientist (Manuel Kukuljan; Chile). The principal goals of the proposed research are to isolate cDNAs corresponding to the Xenopus orthologue of Slo (xSlo). The Slo gene encodes the pore-forming "-subunit of large conductance potassium (BK) channels. In Xenopus embryonic spinal neurons, BK channels undergo a developmentally regulated change in their sensitivity to calcium. By isolating variants of Slo expressed in embryonic spinal neurons during the developmental period of interest, the investigators will examine the possibility that alternatively spliced variants of xSlo are expressed and that these xSlo variants determine the observed developmentally regulated calcium sensitivity of BK channels. There are 3 Specific Aims: 1) isolate the Xenopus laevis orthologue of the Slo gene (xSlo), 2) analyze expression of xSlo and alternatively spliced forms in Xenopus embryonic spinal neurons, and 3) determine the functional properties of xSlo and variants. The proposed experiments combine embryological, molecular and electrophysiological techniques. The majority of the experiments will be carried out at the foreign site. The long-term goal of this research is to obtain molecular entry into developmental pathways that regulate ion channel expression and function.